We used an AutoCom system (http://www.autocomamerica.com
) for the MOTO-ST 8 Hours at Daytona. I have to admit, despite my initial skepticism, it worked really well. We tested it during one practice session and one race at Gingerman in October. At Daytona, you could hear the rider from anywhere on the track. For the rider, it was difficult to clearly hear the crew at high speed on the banking, but not bad in the infield.
It wasn't really that distracting. At worst, my crew chief would say something when I was busy and couldn't talk. I'd just wait to talk back on a straight or when I wasn't in traffic.
The system paid for itself when we had full course caution pace car situations (twice). I was able to work with my crew chief to figure out exactly what I was supposed to do, when the pits were open, etc. Pretty worthwhile for a long endurance race.